[CRIU] [PATCH] link_remap: do not create excessive links for a single file

[Pavel Emelyanov]

On 06/30/2016 08:11 PM, Stanislav Kinsburskiy wrote:
> Currently criu always creates link for each file, considered as "silly-renamed".
> Even in those cases, when file is opened multiple times, it creates one new
> link for each occurrence.
> On restore only one link file is used for all the file descriptors, sharing
> this path. And only this link is removed.

Would you cook a zdtm test showing it?

> The rest of the links are forgotten and abandoned on file system.
> This patch fixed this mess by creating the link only iff it's unique. Or
> skipping this job otherwise.
> 
> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
> ---
>  criu/files-reg.c |   50 ++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 44 insertions(+), 6 deletions(-)
> 
> diff --git a/criu/files-reg.c b/criu/files-reg.c
> index fd36ae9..b1ad271 100644
> --- a/criu/files-reg.c
> +++ b/criu/files-reg.c
> @@ -70,9 +70,11 @@ struct link_remap_rlb {
>  	struct list_head	list;
>  	struct ns_id		*mnt_ns;
>  	char			*path;
> +	char			*orig;
> +	u32			id;
>  };
>  
> -static int note_link_remap(char *path, struct ns_id *nsid)
> +static int note_link_remap(char *path, char *orig, struct ns_id *nsid, u32 id)
>  {
>  	struct link_remap_rlb *rlb;
>  
> @@ -84,11 +86,18 @@ static int note_link_remap(char *path, struct ns_id *nsid)
>  	if (!rlb->path)
>  		goto err2;
>  
> +	rlb->orig = strdup(orig);
> +	if (!rlb->orig)
> +		goto err3;
> +
>  	rlb->mnt_ns = nsid;
> +	rlb->id = id;
>  	list_add(&rlb->list, &remaps);
>  
>  	return 0;
>  
> +err3:
> +	xfree(rlb->path);
>  err2:
>  	xfree(rlb);
>  err:
> @@ -96,6 +105,22 @@ err:
>  	return -1;
>  }
>  
> +static int find_link_remap(char *path, struct ns_id *nsid, u32 *id)
> +{
> +	struct link_remap_rlb *rlb;
> +
> +	list_for_each_entry(rlb, &remaps, list) {
> +		if (rlb->mnt_ns != nsid)
> +			continue;
> +		if (strcmp(rlb->orig, path))
> +			continue;
> +
> +		*id = rlb->id;
> +		return 0;
> +	}
> +	return -ENOENT;
> +}
> +
>  /* Trim "a/b/c/d" to "a/b/d" */
>  static int trim_last_parent(char *path)
>  {
> @@ -725,6 +750,7 @@ static void __rollback_link_remaps(bool do_unlink)
>  		}
>  
>  		list_del(&rlb->list);
> +		xfree(rlb->orig);
>  		xfree(rlb->path);
>  		xfree(rlb);
>  	}
> @@ -781,28 +807,40 @@ static int create_link_remap(char *path, int len, int lfd,
>  		return -1;
>  	}
>  
> -	if (note_link_remap(link_name, nsid))
> +	if (note_link_remap(link_name, path, nsid, *idp))
>  		return -1;
>  
>  	return pb_write_one(img_from_set(glob_imgset, CR_FD_REG_FILES), &rfe, PB_REG_FILE);
>  }
>  
> -static int dump_linked_remap(char *path, int len, const struct stat *ost,
> -				int lfd, u32 id, struct ns_id *nsid)
> +static int dump_linked_remap_type(char *path, int len, int lfd, u32 id, struct ns_id *nsid, RemapType remap_type, bool unique)
>  {
>  	u32 lid;
>  	RemapFilePathEntry rpe = REMAP_FILE_PATH_ENTRY__INIT;
>  
> -	if (create_link_remap(path, len, lfd, &lid, nsid))
> -		return -1;
> +	if (!find_link_remap(path, nsid, &lid)) {
> +		pr_debug("Link remap for %s already exists with id %x\n",
> +				path, lid);
> +		if (unique)
> +			return 0;
> +	} else if (create_link_remap(path, len, lfd, &lid, nsid))
> +			return -1;
>  
>  	rpe.orig_id = id;
>  	rpe.remap_id = lid;
> +	rpe.has_remap_type = true;
> +	rpe.remap_type = remap_type;
>  
>  	return pb_write_one(img_from_set(glob_imgset, CR_FD_REMAP_FPATH),
>  			&rpe, PB_REMAP_FPATH);
>  }
>  
> +static int dump_linked_remap(char *path, int len, const struct stat *ost,
> +				int lfd, u32 id, struct ns_id *nsid)
> +{
> +	return dump_linked_remap_type(path, len, lfd, id, nsid, REMAP_TYPE__LINKED, false);
> +}
> +
>  static pid_t *dead_pids;
>  static int n_dead_pids;
>  
> 
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